Contrast-Enhanced Image-Guided Lead Deployment for Left Bundle Branch Pacing

Authors, Journal, Affiliations, Type, DOI

• Authors: Xi Liu, Hong-xia Niu and Min Gu (joint first authors); Xuhua Chen; Yiran Hu; Minsi Cai; Nixiao Zhang; Junhan Zhao; Xiaohong Zhou; Michael R. Gold; Wei Hua (corresponding); Shu Zhang
• Journal: Heart Rhythm 2021;18(8):1318–1325. © 2021 Heart Rhythm Society
• Affiliations: Cardiac Arrhythmia Center, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing; Cardiac Rhythm and Heart Failure Division, Medtronic plc; Division of Cardiology, Medical University of South Carolina
• Type: Two-phase study — an exploratory derivation phase in 20 patients, then a prospective 1:1 randomized trial in 60 patients with symptomatic bradycardia (May–October 2020), comparing standard implantation with tricuspid valve annulus (TVA) visualization
• DOI: 10.1016/j.hrthm.2021.04.015
• Registration: ChiCTR2100041794. Funding: National Natural Science Foundation of China (82070349); Fundamental Research Funds for Central Universities (3332019047); PUMC Graduate Innovation Fund. Disclosures: Zhou is a Medtronic employee; Gold receives consulting fees from Medtronic and Boston Scientific

Overview

LBBP implantation has no reliable entry-site landmark before the lead is deep in the septum: unlike HBP, there is no LBB potential to find from the right side, and the conventional "W" pattern in V1 is absent in nearly half of successful implants. This study derives one. By injecting contrast to visualise the tricuspid valve annulus in RAO 30°, it finds that 19 of 20 successful lead tips lay within a fan-shaped area centred on the TVA summit, radius 15–50 mm, spanning 110° above to 260° below the summit. A smaller sub-area — 15–35 mm and 110–230° — yielded an LBB potential in 8 of 10 patients and was designated the optimal target. In a randomized comparison, operators using the technique placed the lead directly in that area without searching for a His potential or a W pattern: procedural time fell from 85.5 to 66.8 min, fluoroscopy from 11.1 to 7.8 min, deployment attempts from 2.96 to 2.03, and LBB-potential recording rose from 46.4% to 79.3% — with identical pacing parameters at implant and 3 months.

Keywords

Left bundle branch area; Left bundle branch pacing; Symptomatic bradycardia; Tricuspid valve annulus; Visualization technique

Key Takeaways

The problem

• HBP locates its target by recording the His potential; LBBP cannot — the LBB potential is only recordable after the helix has reached the left side of the septum
• The standard entry-site marker — a "W" pattern in V1 on unipolar pacing — is not observed in nearly half of successful LBBP patients
• The procedure is therefore empirical, and repeated deployment attempts increase the risk of septal injury and perforation

The technique

• TVA visualization: after the LBB lead is deployed (or before, in the guided group), a second C315 His sheath is advanced into the RV and withdrawn with counter-clockwise rotation until its tip lies below the root of the tricuspid septal leaflet in RAO 30°; 10–15 mL of contrast is injected for right ventriculography to outline the annulus and its summit
• Exploratory phase (20 patients):
  • 19/20 successful sites lay within a fan centred on the TVA summit: radius 15–50 mm, angle 110° above to 260° below the summit
  • A smaller green area (area 1) — radius 15–35 mm, angle 110–230° — contained 8/10 patients with a recordable LBB potential
  • The remainder was area 2 (yellow), where LBB potential was infrequent
  • Area 1 is proposed to correspond to the main LBB trunk; area 2 to more distal branches
• Guided implantation: visualise the TVA summit and mark it; place the lead directly in area 1 without searching for a His potential or the W pattern; if 3 attempts fail in area 1, move to area 2; monitor paced morphology during advancement
• Failure definitions (both groups): capture threshold >1.5 V/0.4 ms, fluoroscopy >20 min, or no LBB capture after 5 deployments

Randomized results

• Implant success: 28/30 (93.3%) standard vs 29/30 (96.7%) visualization — not significantly different
• Pacing parameters were unchanged: threshold 0.78 ± 0.26 vs 0.79 ± 0.25 V/0.4 ms; R wave 11.21 ± 4.57 vs 10.22 ± 3.75 mV; impedance 666.43 ± 130.81 vs 677.21 ± 130.69 Ω; LVAT 69.71 ± 7.50 vs 68.48 ± 6.71 ms; paced QRS 112.93 ± 10.84 vs 113.83 ± 10.48 ms
• RBB injury: 6 (21.4%) standard vs 2 (6.9%) visualization — 4 transient and 2 permanent in the standard group, 2 transient and 0 permanent in the visualization group (P = .23 for the comparison)
• QRS behaviour by substrate: in intrinsic bundle branch block, LBBP shortened QRS (155.30 ± 27.50 → 123.00 ± 8.19 ms, P < .01); in narrow QRS it lengthened it (97.83 ± 9.56 → 111.34 ± 9.93 ms, P < .01)
• 3-month follow-up: thresholds 0.77 ± 0.26 vs 0.75 ± 0.22 V/0.4 ms, R waves 11.89 ± 4.44 vs 11.28 ± 3.92 mV, impedances 474.89 ± 77.18 vs 489.41 ± 75.77 Ω — no differences; LVEF and LVEDD unchanged; no procedure-related complications in either group

Area 1 versus area 2 — what the target buys

• Area 1 is a potential-recording zone, not a synchrony zone: LVAT, paced QRS and pacing parameters were identical between areas, but area 1 yielded an LBB potential in 86.5% versus 17.6%
• Area 2 produced a more leftward paced axis, interpreted as more frequent capture of the left posterior fascicular region
• The practical refinements the authors adopted: avoid placing the lead above the horizontal level of the TVA summit (where procedure-induced RBBB was more likely, because the right bundle runs anteriorly), and enter 10–20 mm distal to the TVA (where the endocardium is less thick and penetration is easier)

Limitations of the document

Authors' own stated limitations

• Single centre, relatively small sample, short follow-up; the statistical power was unable to assess differences in success and complication rates
• Patients had preserved LV function and bradycardia indications, so the results may not apply to reduced-LVEF or CRT populations
• The impact of repeated attempts on tissue injury remains unknown — the technique reduces attempts, but the injury avoided was not measured

Additional limitations evident in the study

• The derivation and validation are from the same centre and the same operators. The fan-shaped target was derived from 20 patients at Fuwai and tested immediately afterwards at Fuwai; there is no external validation, and the angular/radial boundaries (15–50 mm, 110–260°) are empirical with no confidence bounds
• Randomisation is described but allocation concealment and blinding are not. Operators could not be blinded to the technique, and the primary endpoint — procedural duration — is sensitive to operator expectation and learning. The 20% effect size assumed in the power calculation was met, but the trial is small (n=60) and the between-group difference in operator experience over the sequential enrolment period is not addressed
• The trial is not powered for the outcomes that matter. Success (93.3% vs 96.7%) and complications (0 vs 0) are indistinguishable at this size, and the RBB injury difference (21.4% vs 6.9%, P = .23) is presented as supportive but is not statistically significant
• The benefit is procedural, not electrophysiological. LVAT, paced QRS, threshold, sensing and impedance were identical; the only electrophysiological gain was more frequent LBB-potential recording, which is a marker of proximity rather than of capture
• The contrast technique has its own costs. It requires a second C315 sheath, 10–15 mL of contrast, and additional fluoroscopy to visualise the annulus. The net fluoroscopy time was lower, but the contrast load, catheter manipulation, and cost are not quantified, and patients with renal impairment were presumably excluded (not stated)
• The target area is anatomically plausible but not proven. Calling area 1 "the main LBB trunk" rests on the higher potential-recording rate and on prior anatomical studies; there is no imaging–histology co-registration in this paper
• The entry-site recommendation (10–20 mm distal to the TVA) is based on operator experience, not on a measured comparison; the paper reports it as a lesson learned rather than a tested variable
• Exclusions remove the populations where the technique would be most valuable: ICD/CRT indications, and by extension most CRT candidates; only 20% had bundle branch block
• Follow-up is 3 months, too short to detect late threshold rise, dislodgement, or perforation
• The "area 2" group is small (17 patients) and the axis difference (P = .02) is one of several uncorrected comparisons
• Rating rationale: rated medium. It is a randomised trial with a clear procedural benefit (shorter procedure and fluoroscopy, fewer attempts, more frequent LBB potential) and identical pacing parameters, which is a genuine contribution. But it is small, single-centre, unblinded, underpowered for safety or success, derived and validated in the same institution, and its benefits are procedural rather than clinical; the anatomical interpretation of the target area is inferential

Key Concepts Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — the technique; this paper supplies a fluoroscopic entry-site method
• concepts/Conduction-System-Pacing — the umbrella category
• Tricuspid valve annulus (TVA) visualization — contrast right ventriculography in RAO 30° to mark the annulus summit
• TVA summit — the reference point from which the LBB target fan is drawn
• Area 1 (green) — radius 15–35 mm, 110–230°; the LBB-potential-rich target, proposed as the main LBB trunk
• Area 2 (yellow) — the remainder of the successful-site fan; more distal branches, more leftward paced axis
• "W" pattern in V1 — the conventional entry-site marker, absent in nearly half of successful implants
• Deployment attempts — the procedural variable the technique reduces
• Procedure-induced RBBB — associated with lead placement above the TVA summit, where the right bundle runs anteriorly
• LBB potential — a proximity marker whose recording rate rose from 46.4% to 79.3%

Key Entities Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — primary concept page
• Fuwai Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing — the investigating centre
• Wei Hua; Shu Zhang; Xi Liu; Hong-xia Niu; Min Gu — the investigators
• Medtronic — the 3830 lead and C315 His sheaths used, and the affiliation of co-author Xiaohong Zhou
• Michael R. Gold, Medical University of South Carolina — co-author
• Gu et al. — the prior TVA-visualization work for HBP that this study adapts
• Elizari — the anatomical description of LBB variants used to interpret area 1
• Heart Rhythm Society / Elsevier — publisher

Wiki Pages Updated

• Created: wiki/sources/contrast-guided-lbbap-hrs-2021.md
• Updated: wiki/concepts/Left-Bundle-Branch-Area-Pacing.md
• Updated: wiki/concepts/Conduction-System-Pacing.md
• Updated: wiki/sourceindex.md
• Updated: wiki/wikiindex.md